The present invention relates to a scanning probe microscope used for accurately measuring a specimen shape and the like.
While semiconductor circuits are highly integrated and are microscopically patterned, there is increasing importance on inspection measurement technologies and failure analysis technologies in semiconductor manufacturing processes. While recording densities of hard disk units are increasing, there is also increasing importance on measurement of microstructure and flatness of magnetic parts of read/write heads, surface roughness of recording media, and stereoscopic shapes based on the striped or dotted structure for further improving recording densities. A scanning probe microscope (SPM) is optimal for these uses. The SPM provides a widely known technique in which a microscopic probe scans with its tip in vicinity to or in contact with a specimen surface so as to measure the specimen surface shape at the atomic level.
In surface shape measurement using the SPM, an inspection region is limited to a bright portion smaller than or equal to several hundreds of micrometers square. When a microscopic area is measured at the atomic level, it is necessary to measure a visual field as narrow as several tens to hundreds of nanometers with an accuracy of atomic level or higher. A mechanical section for probe scanning requires high positioning accuracy. It is necessary to fast observe as wide a range as several tens of micrometers in order to find a measurement region. There is also a need for fast measuring irregularity on the specimen surface in as wide a range as several hundreds of micrometers.
The SPM has the advantage of measuring stereoscopic shapes on the specimen surface at high resolution of approximately 0.1 nanometers. However, the SPM requires much time in positioning and measurement of a measure point and is incapable of providing sufficient measurement throughput. The SPM is not used with a manufacturing line for devices such as semiconductors and hard disk units in line, i.e., during the manufacturing process. The SPM has been mainly used for defect analysis offline. On the other hand, it is expected to provide an inline SPM when a measurement result from the SPM can promptly detect an anomaly in various process apparatuses and the measurement result can be fed back to process conditions for the process apparatuses. In such case, the inline SPM is capable of minimizing defective products and improving the fabrication yield of the manufacturing line. The success of the inline SPM depends on how many measure points the inline SPM can process or measure per unit time. An actual manufacturing line requires processing time shorter than or equal to 20 seconds per unit. The requirement is equivalent to measurement throughput of 30 WPH (wafers per hour).
A piezoelectric element is generally used as an actuator for the mechanical section in order to highly accurately position the SPM probe over a specimen. For example, Japanese Published Unexamined Patent Application No. 2004-303991 describes embodiment of a highly accurate SPM that uses parallel flat plates for three axes X, Y, and Z, drives the plates using piezoelectric elements, measures a probe position using a displacement gauge, and controls the probe position. Patent publication P3544453 discloses the three-dimensional microscopic scan mechanism as another probe drive mechanism for improving the probe positioning accuracy. According to the mechanism, a Y stage is connected to an external frame through an elastic member. An XZ stage is formed in the Y stage so as to be used as an X stage and a Z stage and is connected to the Y stage through an elastic member. Three voice coil motors drive the three-axis stages.
All the stages are integrally formed using the same member. A spindle transmits a drive force of the voice coil motor to the stages. Each spindle is structured to be always pressed parallel to the stage operation direction independently of stage displacement. When only the Y stage operates, for example, all the elastic members connecting the external frame with the Y stage deform evenly and elastically, and apply unnecessary force to the axes of motion other than the Y axis. The probe scan mechanism can accurately control probe positioning independently of the three axes. Japanese Published Unexamined Patent Application No. 2005-347484 describes the method of improving the stage positioning resolution through the use of a piezoelectric element that includes two types of piezoelectric elements connected to each other for fine adjustment and coarse adjustment.
Japanese Published Unexamined Patent Application No. 2004-125540 discloses the SPM configuration for improving the measurement throughput. An approach sensor includes an objective lens, a laser diode, and a photodiode that are placed immediately above a probe. The approach sensor detects a specimen surface position. The specimen surface fast approaches the probe tip position to shorten the time for the SPM to start measurement and improve the SPM measurement throughput. The SPM disclosed in Japanese Published Unexamined Patent Application No. 2005-347484 is configured to place an objective lens immediately above a position where the probe comes in contact with a specimen. An observational optical system detects the measurement position on a specimen. The measurement operation can then start without moving the specimen position. The SPM measurement throughput can be improved.
It is difficult for a conventional SPM to allow the probe to fast scan a wide range and accurately scan a microscopic range at high resolution concurrently. There has been no alternative but to configure the SPM so that it can measure only a narrow range at the sacrifice of operability or it can measure a wide range at the sacrifice of accurate and high-resolution measurement in a narrow range.